The invention relates to a liquid crystal optical device, and more particularly to a liquid crystal optical device having high-speed response characteristics. This high-speed response is obtained by utilizing a liquid crystal material obtained by adding an optically active material to a nematic liquid crystal which exhibits dielectric relaxation when a low frequency signal is applied thereto. In detail, the invention relates to a liquid crystal optical device wherein the liquid crystal material is driven in a time-sharing mode.
In recent years, information processing techniques have made remarkable advances. In view of these advancing techniques, various types of output devices, such as high-density and high-speed printing devices are required. In addition to high-speed, high-quality level printing is also required. In order to satisfy these above-mentioned needs, a laser-beam printer (LBP) or an optical fiber tube (OFT) printer using electrophotography and light writing has been placed into actual use on printing devices. However, the high price of both LBP and OFT prevent them from being widely accepted in spite of the strong demands for their outputs.
With this in mind, the present invention is aimed at providing a high-speed liquid crystal light valve which has been difficult to produce to date due to various problems. Such a light valve can be utilized in a light writing device of the type mentioned above. In addition, the circuit construction for driving the liquid crystal light valve can be simplified by improving the driving method which will permit cost to be reduced further. The use of liquid crystal display devices is also rapidly increasing. Thus, various studies of time-sharing drive for reducing the number of driving devices and the wiring costs are also under consideration. At the present time, time-sharing drive of about 1/16 duty has been attempted on a practical level. However, time-sharing drive of about 1/32 through 1/64 duty has only approached the experimental level.
Conventionally, the time-sharing drive of a liquid crystal is performed by the generalized A C amplitude selective multiplexing method based on the cumulative response effect. The largest duty N is determined by the ratio of ON voltage to OFF voltage by the following equation: EQU .alpha.=(.sqroot.n+1/29 n-1).sup.1/2
Attempts by the present inventors are directed upon making .alpha. smaller and approaching 1; namely to make the threshold steep and obtain the desired results.
Presently, however, fluctuation of the threshold voltage depends upon thermal distribution within a liquid crystal panel of large volume. This fluctuation is larger than the threshold voltage width determined by .alpha.. Thus, portions of poor quality occur within the panel when the thermal distribution differences within the panel are somewhat more than 2.degree. C. This occurs even though the voltage is controlled precisely in accordance with the temperature deviation. In other words, the attempts for making .alpha. smaller and making N larger are meaningless when one considers the actual temperature distribution range under actual usage conditions. Accordingly, it would be desirable to provide a time-sharing drive which is different than the conventional time-sharing driving method which utilizes the generalized A C amplitude selective multiplexing method based on cumulative response effect. In other words, the present invention seeks to provide a method for increasing N as high as one desires, and which does not depend upon temperature deviation.